Who was the youngest pope?

The youngest Pope to be acknowledged by the Vatican was John XII, who reigned from 955 to 963. He was approximately 18 years old at the time of his election, which was carried out to honor the dying wish of his father, Alberic II.

John XII was the youngest Pope in history, and his reign was not tranquil. Shortly after his installation as the spiritual and temporal authority of Rome, John was accused of sacrilege, simony, perjury, murder, adultery and incest. He is not known to have denied the charges, but he did excommunicate the bishops who sought to impeach him. Shortly after mounting a successful siege to retake Rome, the 25-year-old Pope mysteriously died.